1. Field of the Invention
The present invention relates generally to magnetic sensing elements for use in magnetic sensors and hard disks. In particular, the present invention relates to a method for manufacturing a magnetic sensing element having improved magnetic field sensitivity.
2. Description of the Related Art
FIG. 38 is a cross-sectional view of a magnetic sensing element made according to a known manufacturing method when viewed from a face of the element opposing a recording medium. This face is hereinafter referred to as the “opposing face”.
The magnetic sensing element shown in FIG. 38 is of a spin-valve type which is a type of giant magnetoresistive (GMR) element utilizing the giant magnetoresistive effect. The spin-valve magnetic sensing element detects a recorded magnetic field on a recording medium such as a hard disk.
As shown in FIG. 38, this spin-valve magnetic sensing element comprises: a composite 8 comprising a substrate 1, an underlayer 2, a first antiferromagnetic layer 3, a pinned magnetic layer 4, a nonmagnetic layer 5, a free magnetic layer 6, and a protective layer 7; a pair of ferromagnetic layers 9 disposed at two sides of the composite 8; a pair of second antiferromagnetic layers 10 formed on the ferromagnetic layers 9; and a pair of electrode layers L.
Generally, the first antiferromagnetic layer 3 and the second antiferromagnetic layers 10 are made of an Platinum-manganese (Pt—Mn) alloy. The pinned magnetic layer 4, the free magnetic layer 6, and the ferromagnetic layers 9 are made of a nickel-iron (Ni—Fe) alloy. The nonmagnetic layer 5 is made of copper. The underlayer 2 and the protective layer 7 are made of tantalum. The electrode layers L are made of chromium.
The pinned magnetic layer 4 is set to a single-magnetic-domain state in the Y direction in the drawing due to an exchange anisotropic magnetic field with the first antiferromagnetic layer 3. The Y direction is the direction of the magnetic field leaking from the recording medium and is also the height direction.
The ferromagnetic layers 9 are set to a single-magnetic domain state in the X direction by an exchange anisotropic magnetic field with the second antiferromagnetic layers 10. The ferromagnetic layers 9 come into contact with the free magnetic layer 6 at junctions J to make a continuous ferromagnetic unit. Thus, the free magnetic layer 6 is set to a single-magnetic-domain state in the X direction by an exchange bias method. The advantage of the exchange bias method is that no surface magnetic charge is generated at the two sides of the free magnetic layer 6, i.e., the junctions J and the demagnetizing field in the free magnetic layer 6 can be minimized.
In the magnetic sensing element, a detecting current, i.e., a sense current, is fed from the electrode layers L to the free magnetic layer 6, the nonmagnetic layer 5, and the pinned magnetic layer 4 via the second antiferromagnetic layers 10 and the ferromagnetic layers 9. The moving direction of the recording medium such as a hard disk is the Z direction. When a leakage magnetic field is applied from the recording medium in the Y direction, the magnetization direction of the free magnetic layer 6 shifts from the X direction toward the Y direction. Such a shift in the magnetization direction of the free magnetic layer 6 relative to the pinned magnetization of the pinned magnetic layer 4 changes the electrical resistance. This phenomenon is known as the magnetoresistive effect. The change in voltage cause by this change in electrical resistance helps detect the leakage magnetic field from the recording medium.
In manufacturing the magnetic sensing element shown in FIG. 38, the underlayer 2, the first antiferromagnetic layer 3, the pinned magnetic layer 4, the nonmagnetic layer 5, the free magnetic layer 6, and the protective layer 7 are deposited on the substrate 1. Each of these layers has a uniform thickness. Subsequently, specific portions of the deposited layers are ion-milled to make the composite 8 shown in FIG. 38. The ferromagnetic layers 9 are then deposited at the two sides of the composite 8 so that the ferromagnetic layers 9 come into direct contact with side faces 8a of the composite 8. Finally, the second antiferromagnetic layers 10 and the electrode layers L are formed on the ferromagnetic layers 9.
In the magnetic sensing element shown in FIG. 38, the side faces 8a of the composite 8 are formed by milling, as described above. When ferromagnetic layers 9 are directly formed on surfaces formed by milling, such as the side faces 8a, it is difficult to make a continuous ferromagnetic unit comprising the ferromagnetic layers 9 and the bias layers 6 in contact with each other at the junctions J. Thus, it is difficult to stably set the free magnetic layer 6 into a single-magneticdomain state in the X direction.
Moreover, since the junctions J between the ferromagnetic layers 9 and the free magnetic layer 6 are arranged above the side faces 8a of the composite 8, it is difficult to magnetically couple the ferromagnetic layers 9 and the free magnetic layer 6 at the junctions J. Thus, it is difficult to stably set the free magnetic layer 6 into a single-magnetic-domain state in the X direction.
If an angle θ1 of the side face 8a of the composite 8 is minimized to stabilize the magnetic coupling between the ferromagnetic layers 9 and the free magnetic layer 6 at the junctions J, then it would be difficult to form the free magnetic layer 6 at a predetermined width in the track width direction (the X direction).
As described above, the known magnetic sensing element shown in FIG. 38 employing the exchange bias method suffers from the problem that a stable longitudinal bias cannot be stably applied to the free magnetic layer 6, thereby preventing the free magnetic layer 6 from entering into a single-magnetic-domain state in the X direction.
Further, to ensure the coupling of the ferromagnetic layers 9 and the free magnetic layer 6, the thickness of the ferromagnetic layers 9 must be increased. However, thick ferromagnetic layers 9 decreases the magnitude of the unidirectional anisotropic magnetic field of the ferromagnetic layers 9. Hence, a stable and sufficient longitudinal bias cannot be applied to the free magnetic layer 6. Moreover, when the thickness of the ferromagnetic layers 9 is increased, insensitive regions are generated at the two sides of the free magnetic layer 6, causing degradation of the read sensitivity.